1. Field of the Invention
This invention relates to the field of wheel suspensions, and particularly to wheel suspension systems that independently support the wheels of a trailer, semi-trailer of other vehicle in which a wide and low cargo floor is desired.
2. Description of the Prior Art
Virtually every commodity in the market today is, at one time or another, transported by truck, often in a tractor-trailer rig. For long distance transport, the trailer, or semi-trailer as it is often called, is frequently carried by rail car.
It is axiomatic that the larger the cargo space for a fully loaded van or trailer, the lower the per-mile transportation cost for the transported commodities. There are factors, however, which limit van and trailer size. Various governmental regulations dictate the maximum dimensions of highway vehicles. And, of course, for trailers being transported by rail, the dimensions of the standardized rail car dictate the maximum dimensions of the trailer.
In the most common form of piggyback trailer rail transport, each rail car carries two trailers. The standard rail-transportable trailer has a maximum length of approximately 45 feet, a maximum width of approximately 102 inches, and a maximum height above the ground of approximately 162 inches. For the reasons mentioned above, these dimensions are not to be exceeded. It is, thus, impractical to increase cargo space by increasing the overall dimensions of the trailer.
Heretofore, in most rail-transportable trailers, the floor of the cargo space, i.e., the bottom of the trailer body, is several feet off the ground to clear the rear wheels, axles, and suspension of the tractor and the rearwardly disposed wheels and suspension of the trailer.
The introduction of airbag suspension systems for tractor-trailer rigs has somewhat reduced the distance between the trailer floor and the road surface required to clear the tractor and trailer suspension systems. But the increase in cargo capacity of trailers so equipped has been quite small. U.S. Pat. Nos. 3,078,104, granted Feb. 19, 1963, to W. G. Chalmers for INDEPENDENT REAR SUSPENSION FOR SEMI-TRAILERS, and 3,140,880, granted Jul. 14, 1964, to L. D. Masser for SUSPENSION FOR AUTOMOTIVE VEHICLES, show representative pneumatic suspension systems.
It has also been proposed to utilize some of the space between the ground and the bottom of the trailer body by equipping the body with a depending support structure between the wheels of the trailer and the wheels of the tractor to gain auxiliary cargo space. U.S. Pat. No. 3,884,502, granted May 20, 1975, to R. F. Wagner for SEMITRAILER OR THE LIKE, discloses a trailer with this modification. The disadvantage here is that, although the additional support structure adds cargo space, that space is not in communication with the interior of the trailer and, therefore, does not increase the size of the main cargo compartment. The size of commodities that can be carried remains restricted.
Another approach to increasing the cargo capacity of trailers has been the use of the so-called "drop frame" for the trailer body. In this construction, the floor of the cargo compartment is dropped close to the road surface between the suspension apparatus of the tractor and the suspension apparatus of the trailer and also possibly for a short distance to the rear of the trailer suspension. Again, the cargo capacity has been increased, but there are shortcomings to this design. Principal among these is the hump, or rise, in the floor of the cargo compartment required to clear the wheels, axles, and suspension components of the trailer. This makes it impossible to load the trailer with a forklift truck through the rear door of the trailer from a conventional loading dock. The addition of doors to the sides of the trailers, of course, increases the cost of the trailer, and those doors often are not accessible from the loading dock.
U.S. Pat. No. 4,619,578, granted Oct. 28, 1986, to J. H. Routledge for RETRACTABLE WHEEL SUSPENSION APPARATUS, discloses an interesting arrangement for utilizing the space between opposite wheel assemblies of a container carrier. The tractor disclosed in that patent pulls a horizontally disposed, U-shaped frame which is open at the rear so that the frame can be backed under and around a container. The two legs of the frame are supported by pneumatic suspension systems whereby the wheels of one leg are suspended independently of the wheels on the opposite leg. Because there are no through-axles between the wheels on one frame leg and the wheels on the other leg, the space between the opposite wheels can be occupied by the cargo container. The system disclosed in the Routledge Patent is simply too complex and too expensive to be utilized on the common transport trailer.
In U.S. Pat. No. 4,032,167 issued to Chereda on Jun. 28, 1977, there is disclosed a trailer for transporting motorcycles. The Chereda trailer includes a rigid, horizontal frame upon which is mounted a pair of opposed wheels. The two wheels are secured to fixed spindles bolted to the frame. No provision is made for suspending the wheels other than by this rigid attachment, and the Chereda trailer would therefore suffer from the disadvantages of the rigid mounting of the wheels to the load-carrying frame. Heavy vehicle suspension is described in U.S. Pat. No. 4,718,692 issued to Raidel on Jan. 12, 1988. The Raidel suspension is typical of prior art systems which use pairs of pivoting arms to support a through axle that extends the width of the vehicle below the vehicle frame.
One of the problems confronting the prior art has been the lack of strength and stability for suspension systems which do not include full-width axles. Devices such as the Chereda trailer have been suitable for light-load applications, but are not practical for heavy use since the rigid attachment of the wheels to the trailer frame causes considerable forces to be transmitted to the frame. Conversely, the pivoting arm suspensions, such as in the Raidel system, have been found applicable to heavy use when incorporating a through axle. Absent the through axle, however, the pivoting arm devices of the prior art have not been designed to provide adequate strength and stability, particularly in terms of the lateral forces transmitted to the suspension upon turning of the vehicle.
Various other devices have been proposed in the prior art, which are characterized by the foregoing limitations. In U.S. Pat. No. 4,580,798 issued to Roelofs on Apr. 8, 1986, there is described an air suspension system for the rear end of a motor home. As with similar prior art devices, the Roelofs suspension system includes a pivoting arm for support of the wheel which is mounted to a through axle. Comparable devices including axles extending underneath the vehicle frame are disclosed in U.S. Pat. Nos. 4,060,145 issued to Kingman, et al. on Nov. 29, 1977; 3,214,047 issued to Moye on Oct. 26, 1965; 4,422,667 issued to Perry on Dec. 27, 1983; 4,666,181 issued to Wegner on May 19, 1987; 4,063,611 issued to Anderson on Dec. 20, 1977; 3,704,898 issued to Schmadt on Dec. 5, 1972; 3,140,880 issued to Masser on Jul. 14, 1964; 3,884,502 issued to Wagner on May 20, 1975; 4,619,578 issued to Routledge on Oct. 28, 1986; and, 3,829,118 issued to Gouirand on Aug. 13, 1974.
An underslung wheel suspension system including a pivoting arm supporting a wheel on a spindle is described in U.S. Pat. No. 3,356,386 issued to Taylor on Dec. 5, 1967. The trailer frame including wheels secured to elevated end portions of a drop axle is described in U.S. Pat. No. 4,095,818 issued to Smith on Jun. 20, 1978. In U.S. Pat. No. 3,282,603 issued to Barth on Nov. 1, 1966, there is described a vehicle frame which includes independently mounted wheels rotatably mounted onto supports rigidly fixed to the vehicle frame. Other independent wheel suspensions utilizing pivoting arms for supporting the wheels are described in U.S. Pat. Nos. 2,507,980 issued to Knapp on May 16, 1950; and 3,078,104 issued to Chalmers on Feb. 19, 1963.
Other vehicle suspension assemblies are described in U.S. Pat. Nos. 4,736,965 issued to Smith on Apr. 12, 1988; 3,773,348 issued to Davis on Nov. 20, 1973; 4,468,739 issued to Woods, et al. on Aug. 28, 1984; 3,746,363 issued to Borns on Jul. 17, 1973; and, 4,470,165 issued to Scheuerle on Sept. 11, 1984.
There continues to be a need, therefore, for a trailer suspension apparatus which will permit the floor of the trailer body to be lowered closer to the roadway surface and to be substantially flat from the rear of the trailer through the wheel region of the trailer.